Changes in spatial distribution during the life history of a tropical tree, Scaphium macropodum (Sterculiaceae) in Borneo

We studied the spatial distribution of fruits and plants, mortality and growth rates of Scaphium macropodum (Sterculiaceae) in four 1-ha plots in a tropical rain forest in West Kalimantan, Indonesia. The species is a large deciduous tree and produces wind-dispersed fruits on defoliated twigs. The density of dispersed fruits on the ground decreased with increasing distance from a parent tree. The area under the parent's crown had the highest density of the fruits and the highest mortality of the seedlings immediately after germination. Consequently, the density of the established seedlings peaked 14 m from the tree which is outside its crown. Thick litter mainly from the parent tree seemed to physically prevent the seedlings' root from reaching the soil surface and caused the high mortality. Juvenile and mature trees distributed exclusively, suggesting that regeneration is the most successful outside of the crown of mature trees. Saplings under canopy shade did not grow well. Scaphium macropodum is hypothesized to require a gap for seedling growth and successful regeneration, whereas it can germinate and last under closed canopies as suppressed seedlings or saplings.